The present invention relates to a protective circuit apparatus in the form of a two to three wire converter circuit. More particularly, the present invention relates to a protective circuit apparatus in which power connection is made to an electrical device only if the high and neutral lines of an electrical supply are properly connected to the high and neutral lines, respectively, of the electrical device.
For a number of years, the accepted way of protecting against insulation failure in electrical devices has been grounding. This applies to all types of electrical devices from hand tools, such as electric drills and saws, to appliances, such as refrigerators and portable dishwashers. The grounding is intended to be carried out by providing an extra wire connected to the conductive parts of the electrical devices' housing. The wire runs through the cord to a third prong that slips into a grounded socket located adjacent the high and neutral sockets of an electrical supply outlet. In the case of insulation failure, for example in an electrical motor, the current runs from the windings at the motor through the motor housing to the electrical devices' housing. If a proper ground is provided for the electrical devices' housing, this current is harmlessly carried to ground until a fuse burns out or a circuit breaker trips.
However, it is estimated that fewer than 20% of all homes in the United States are equipped with receptacles that accept the three-prong plugs of electrical devices supplied with the third housing ground wire. Consequently, many home handymen and even some professionals clip off the third prong. In other cases, the housing ground wire of the electrical device may be broken in the electrical devices power cord or in an extension cord which may be used with the electrical device. The housing ground wire may also become disconnected at the connections. Under these circumstances, the user of the electrical device, whether it be a hand tool or some other appliance, will not be aware of the fact that the housing of the electrical device is not connected to ground. This will not become apparent until an insulation failure occurs and the housing or casing of the electrical device becomes electrically hot. At that point, it is too late since the user may be shocked, possibly resulting in other secondary injuries such as falling from a ladder, or even be electrocuted.
Even in the industrial setting where the electrical supply receptacles are provided with three sockets, one corresponding to ground, the user of an electrical device is not entirely safe in the absence of the present invention. For example, the housing ground wire in the cord of the electrical device or an extension cord may be broken. Furthermore, the ground connection to the ground socket of the electrical receptacle or outlet may be broken or may never have been properly connected. Again, the user of an electrical device connected to such a defective third wire ground system will not become aware of the defect until it is too late.
The present invention overcomes the above problems by enabling the connection of the housing or the housing ground wire to the neutral line of the electrical supply. The neutral line of an electrical supply is connected to ground. If a break or other discontinuity occurs in the neutral line, it becomes readily apparent to the user of the electrical device since power flow to the electrical device ceases.